The present disclosure relates to an exemplary method for process diagnosis in the coating, particularly the paint-coating, of workpieces such as vehicle bodywork or parts thereof and a corresponding exemplary rotary atomizer arrangement.
Known electrostatic rotary atomizers typically operate with direct charging of the coating material, with the electrically conducting part of the atomizer being placed at a high voltage, so that the coating material can be charged by an electrode device comprising all the electrically conductive parts such as the bell plate, paint tube, screw threaded fixings, etc., with which said material comes into contact. Alternatively, external charging of the coating material with external electrodes is possible.
Conventional rotary atomizers may generally contain a pneumatic drive turbine for the bell plate forming the spraying element, the rotary speed of which can be measured by, for example, optical sensing of rotating markings and transmission of the sensed impulses via optical waveguides, and kept constant by means of a control circuit by controlling the drive air (DE 43 06 800 C2 and EP 1 388 372 B1), although herein the problem exists that, at the start of a coating procedure, when the conventionally provided main needle valve 24 controlling the outflow of coating material from the atomizer, due to the inertia of the control system, the rotary speed can initially fall relatively severely, which leads to coating faults and can only be corrected by complex additional measures.
With the main needle valve 24, in order to compensate with control technology for switching faults such as temporal delays or shifts caused, for example, by component wear, and resulting in coating faults, particularly when a painting robot makes rapid movements, it is necessary to monitor the switching times. For this purpose, it is generally known to detect and evaluate the switch settings with optoelectronic sensors and optical waveguides (EP 1 245 291 B1). However, the waveguides do not always transmit the sensor signals reliably due to interfering or disrupted interfaces and, due to the constant bending movements in a paint robot, have only a very limited lifespan and, due to their arrangement in the robot, can also only be exchanged or replaced with significant effort. In some cases, also, signal evaluation can be too slow for optimum fault compensation.
Furthermore, a variety of process faults and other fault conditions cannot be detected at all during painting operation due to a lack of suitable sensors. Typical faults include, for example, the mounting of an incorrect bell plate, or the complete lack of a bell plate, contact between the bell plate and the workpiece or other surrounding objects, imbalance in the bell plate, bearing wear or incorrect or even completely lacking bearing air in the air bearings usually provided for the bell plate shaft of rotary atomizers and incorrect volume flow rate of the coating material or changes in the viscosity or other properties thereof.
It is generally known to replace the air turbine currently in common use with an electric drive motor for the air-mounted bell plate shaft of a rotary atomizer, e.g., as provided in WO 2005/110613. However, known rotary atomizers generally suffer from the same problems described above. Furthermore, known rotary atomizers generally suffer from the problem mentioned above that, in the case of electrostatic coating, it may be necessary to place the entire rotary atomizer at a high voltage, e.g., on the order of 100 kilovolts (kV). An electric drive motor and the control system therefore cannot be used without further measures in an electrostatic rotary atomizer with direct charging of the coating material.
The voltage separation measures generally required with an electrostatic rotary atomizer for the electric motor-drive of a bell plate and for signal transmission are generally described in the German patent application 10 2007 004 819.1 dated 31 Jan. 2007, the entire contents of which is hereby expressly incorporated by reference in its entirety.
Based, in particular, on known rotary atomizers with conventional air turbines, an exemplary method is provided for process diagnosis and/or for highly dynamic control of parameters of the coating process or of the motor with which one or more of the above-mentioned fault conditions can be recognised as quickly and reliably as possible, so that the required countermeasures can be implemented in a timely manner.